Field of the Invention
The present invention generally relates to graphics processing and more specifically to early sample evaluation during coarse rasterization of primitives.
Description of the Related Art
Conventional graphics processing pipelines perform rasterization of primitives in two stages. The first stage is coarse rasterization that identifies one or more pixel tiles in screen space that are covered by a primitive. The second stage is fine rasterization. During fine rasterization, the pixel tiles identified during coarse rasterization are processed to determine which samples are covered by the primitive.
One drawback to such an approach is that small primitives may be identified by the coarse rasterizer as covering a pixel tile when, in fact, no samples within the pixel tile are actually covered by those small primitives. For example, when a small primitive lies on a boundary between two pixel tiles, the small primitive may be identified by the coarse rasterizer as covering two pixel tiles when, in fact, samples may only be covered within one of the two pixel tiles. Therefore, the fine rasterizer processes some pixel tiles that do not actually include even at least one covered sample. Processing pixel tiles that do not include a visible portion or a primitive is undesirable.
Accordingly, what is needed in the art is an approved approach for identifying pixel tiles that are covered by small primitives during coarse rasterization.